1. Field of the Invention
The present invention relates to an optical disc recording method and an optical disc drive apparatus for driving/controlling an optical modulation waveform when recording information on an information recording medium.
2. Description of the Prior Art
As recordable optical discs, a large number of optical discs such as CD-R/RW, DVD-RAM, DVD±R/RW, Blu-ray Disc (BD)-R/RE, HD DVD have been commercialized and have widely spread among public. In a recordable optical disc apparatus, correction of recording power is performed while recording user data on each medium by using a method called an Optimum Power Control (abbreviated as an OPC), in order to record user data constantly at suitable recording power which would vary due to variable factors such as a temperature, a wavelength of light source, production variation of media and the like.
As OPC methods, the followings are known.
(1) An OPC Method Mainly Used for Write-Once Discs
As an example of an OPC method using asymmetry, Japanese Patent Application Laid-open No. Hei 6-139574 discloses an OPC technique using a method in which an asymmetry of repetitive signals of a shortest mark and space is made equal to an asymmetry of repetitive signals of a longest mark and space.
(2) OPC Methods Mainly Used for Re-Writable Discs
As an example of an OPC method using a signal modulation (or reflectance), Japanese Patent Application Laid-open No. 2000-306241 discloses an OPC technique using a method in which recording power is figured out by multiplying power by a coefficient, the power causing a change in reflectance caused by a change in recording power to be maximized. Furthermore, Japanese Patent Application Laid-open No. 2003-067925 disclose an OPC technique using a method in which recording power is figured out by using a gradient of a change in the degree of modulation caused by a change in recording power, or a gradient of a change in a γ-value.
FIG. 1 is a schematic view for describing a γ-method. In this respect, the γ-value represents a value normalized using a rate of change in the modulation and that of recording power. In FIG. 1, a solid line represents the modulation, and a broken line represents a curve describing derivative values thereof. The modulation increases as the power increases, and there is power Ptarget where the modulation sharply increases as a mark is formed. This is a method for figuring out optimum power PWO by multiplying Ptarget by ρ, since the power obtained by multiplying the power around Ptarget by a coefficient causes a margin to be maximized. This method is an index which is not sensitive to a setting offset of recording power.
As for an index of the same kind, there is a so-called κ-method. Japanese Patent Application Laid-open No. 2002-298357 describes the κ-method which is recommended in specification of BDs. A recording power control method using the κ-method is to control an optimum recording power according to: a relational characteristic between recording power figured out by trial writing and the modulation figured out from the amplitude of a readout signal of the signal recorded in the trial writing; and values of Ptarget, Mind, κ and ρ which are set in an optical disc in advance.
FIG. 2 are schematic diagrams for describing the c-method. Optimum recording power Popt is figured out as follows. First, find an estimation value within a range around the set recording power Ptarget corresponding to a specified modulation Mind on the optical disc, by calculating an equation, Sm=Mm×Pwm, as one of relational characteristics between a plurality of kinds of recording power Pwm set in trial writing, and the modulation Mm found by using the amplitude of a readout signal of a signal recorded at each Pwm. Then, find recording power Pthr in the range at which the modulation becomes zero when the relational characteristic between Pwm and Sm is linearly approximated. Finally, find the optimum recording power Popt by calculating Popt=κ×ρ×Pthr by using the previously-found Pthr and the parameters κ and ρ of the optical disc.